Involvement of Actin-Related Proteins in ATP-Dependent Chromatin Remodeling

Abstract

Actin-related proteins (Arps) and conventional actin are enigmatic components of many chromatin-remodeling enzyme complexes. The yeast INO80 ATP-dependent chromatin-remodeling complex contains stoichiometric amounts of Arp4, Arp5, Arp8, and actin. Here we have revealed functions of Arp5 and Arp8 by analysis of mutants. arp5 Delta and arp8 Delta mutants display an ino80 Delta phenotype. Purification of INO80 complexes from arp5 Delta and arp8 Delta cells shows that protein complexes remain intact but are compromised for INO80 ATPase activity, DNA binding, and nucleosome mobilization. The INO80 (arp8 Delta) complex is strikingly deficient, not only for the Arp8 subunit, but also for Arp4 and actin, suggesting an ordered assembly of Arps. Binding of Arp8 to the INO80 complex requires an N-terminal region of Ino80 adjacent to the conserved ATPase domain. GST-Arp8 binds preferentially to histones H3 and H4 in vitro, suggesting a histone chaperone function. These findings show direct involvement of Arps in the chromatin-remodeling process.

INO80 subfamily of chromatin remodeling complexes

“…Recently, it was shown by the Dutta group that Rvb proteins are essential for the chromatin remodeling activity of INO80.com [17]. They further found that loss of Rvb proteins leads to the loss of Arp5, a functionally important subunit of INO80.com [10]. Their in vitro studies reveal that Rvbs and Arp5 associate in a complex and the interaction is Ino80 and ATP dependent [17].…”

“…Despite increasing evidence suggesting that actin is in the nucleus and may play roles in many nuclear functions, the research on nuclear actin has been stalled by the lack of unambiguous demonstrations of an actin function in the nucleus both in vivo and in vitro. Previous studies appear to suggest that the INO80 complex contains a sub-complex consisting of actin, Arp4, Arp8 and Taf14, that associating with the ΔN domain [10] of the Ino80 ATPase. Interestingly, all subunits of this actin/Arp sub-complex, including the ΔN domain of the Ino80 ATPase are evolutionarily conserved, suggesting that this sub-complex represents a unique and evolutionarily conserved module used throughout the yeast INO80 complex and orthologous INO80 complexes in higher organisms.…”

“…Arp5 and Arp8 have so far only been found in INO80.com. Arp5 appears to associate with the complex independently of any other subunit, while Arp8 is necessary for the inclusion of Arp4 and actin [10]. The functions of Arp5 and Arp8 appears to be important for the process of chromatin remodeling, since it has been shown that the phenotypes of arp5Δ and arp8Δ are similar to that of ino80Δ.…”

“…The functions of Arp5 and Arp8 appears to be important for the process of chromatin remodeling, since it has been shown that the phenotypes of arp5Δ and arp8Δ are similar to that of ino80Δ. In vitro DNA binding, nucleosome mobilization, and ATPase activities of the mutant INO80 complexes lacking Arp5 or Arp8 are compromised [10]. Although all Arps contain the 'actin fold' domain, which includes putative ATP-binding sites, Arp4 is the only one has been shown to bind to ATP [22].…”

“…Although all Arps contain the 'actin fold' domain, which includes putative ATP-binding sites, Arp4 is the only one has been shown to bind to ATP [22]. Moreover, ATP binding site mutants of Arp7, Arp9 (subunits of SWI/SNF and RSC), Arp5, and Arp8 do not show observable phenotypes [10,23], suggesting that the ATP binding site of these Arps are dispensable for their functions in chromatin remodeling.…”